The Presentation

On

“TEXTILE COATING”UNDER THE GUIDANCE OF

Prof. (Dr.) M.D.TELIBY

Omkar S. ParmajResearch scholar in

Institute of chemical technology Mumbai

INTRODUCTION Coating has now become a very important technique for adding value

to textiles.

Coating enhances and extends the range of functional performance

properties of textiles.

The use of these techniques is growing rapidly as the applications for

technical textile material has become more diverse.

The key to success in textile coating and lamination depends upon the

application of appropriate technology using advanced machinery.

DEFINITION Coating is an application of an appropriate chemical system to form

a layer of a coating compound on the substrate.

Coating is a process in which a polymeric layer is applied directly

on one or both the surfaces of the fabric.

Depending upon the end-use, heavy-duty technical textile coatings

may be applied.

Unlike woven textile materials now coating is being done on other

textile substrates also such as warp-knitted, weft-knitted and

nonwovens.

COATING FORMULATIONS Formulation contain a wide range of chemicals

depending upon :

Nature of polymer

Necessary additives for the specific end-use.

Whether coating has to be foamed prior to

application.

Type of coating machinery to be used.

POLYMER USED FOR COATING

Polyvinyl chloride (PVC) Polyvynilidene chloride

(PVDC) Polyurethane (PU) Acrylic Ethylene vinyl acetate

(EVA) Poly tetra fluoro ethylene

(PTFE) Styrene butadine

rubber(SBR) Natural rubber (NR) Silicone Polyolefins , LDPE, HDPE,

Polypropylene

PHYSICAL FORMS OF COATING COMPOUNDS

Solvent based systems

Waterbased systems-dispersions and emulsions.

100% solids materials -Film, Powder, Hot Melt.

COATING PROCESS

Process flow diagram of coating

SUBSTRATE A wide range of textile materials is used as substrates for coated fabrics.

Woven Knitted Nonwoven materials

Cotton, Rayon, Nylon, Polyester and blends such as of polyester with cotton or rayon are used as substrate.

Polyester is the most popular in staple form for nonwoven material and also in spun form for woven material.

Polypropylene is emerging as the fibre of choice because of its low specific gravity, strength properties, chemically inert nature and low cost.

SELECTION OF FABRIC

The following aspects need to be considered: Strength and modulus  Creep behaviour Resistance to acids and chemicals  Adhesion requirement Resistance to microbiological attack  Environment of use  Durability  Dimensional stability  Cost

PARAMETERS for uniform COATING

• The parameters necessary for uniformity in coating add-on are as

follows:

Substrate tension

Viscosity of the coating material

Substrate uniformity and porosity

Any variation in these parameters may lead to a non uniform coating.

The coating range is limited to about 0.02 to 0.5 mm thickness.

METHODS OF APPLICATIONS

The technique that is selected for any given product will be

dependent upon a number of factors such as:

Required coat-weight.

The nature of the compound to be applied in terms of its

viscosity and other physical characteristics.

The degree of penetration required into the substrate.

Cost that can be accepted in the end-product.

COATING METHODS

Direct Coating

Foamed And Crushed Foam

Coating

Transfer Coating

Hot Melt Extrusion Coating

Calender Coating

Rotary Screen Coating

Spray Coating

Dry Powder Coating

Curtain Coating

Slot Die Or Extrusion Coating

Mayer Rod Coating

Kiss Roll Coating

Gravure Roll Coating

Reverse Roll Coaters

DIRECT COATING Direct application of coating fluid is done on to the textile fabric by

uniform spreading of coating by the means of a fixed knife. The gap between the bottom of the knife and the top of the fabric controls

the thickness of the coating. The main techniques used are as follows:

Knife on air Knife over roller

Direct coating uniformity depend upon: Shape of knife Angle of knife to fabric Position of knife

KNIFE ON AIR

This type of knife coating is a blade over air, or floating knife process.

The knife is fixed above the substrate. The doctor blade presses the upper surface of the substrate and

forces the coating layer to penetrate into the substrate. The amount of coating applied is controlled by fabric tension and

depression of the knife . The sharpness of the blade, alignment angle and degree of depression

into the substrate influence the amount of coating applied.

KNIFE ON ROLLER

In this process knife blade is suspended above a roller.

The roller can be steel or rubber coated.

The knife does not touch the substrate directly and there

is a gap between substrate and knife which controls the

thickness of the coating.

FOAMED AND CRUSHED FOAM COATING

The method can apply polymer to Woven fabrics, Knitted fabrics, fabric produced from spun yarns or fabrics of an open construction which cannot generally be direct coated.

Fabrics of a general open construction which cannot generally be directly coated.

Foam, which is rather like shaving cream, sits on the top of fabric and Crushed by roller and coat the fabric.

Fabric become much softer handles and better drape than can generally produced by direct coating.

Application: Apparel goods, floor coverings, wall coverings ,black-out curtains and curtain linings .

FOAMED AND CRUSHED FOAM COATING

TRANSFER COATINGThe principle of transfer coating is first to spread the polymer on to

release paper to form a film and then to laminate this film to the fabric. The process is divided in few steps such as:

Coat the resin (which will become the top layer) on to the transfer paper and evaporate off the solvent.

Coat on the second layer, which will become the base layer (and is actually the adhesive which joins the top layer to the fabric).

Lay the fabric on top of the coating, nip together, evaporate the solvent and crosslink the two layers together.

Peel the coated fabric off the release paper. Application: footwear, gloves and waterproof mattress covers.

Woven velvet automotive seat fabric,

TRANSFER COATING

HOT MELT EXTRUSION

COATING

This method is used for thermoplastic polymers such as polyurethane, Polyolefins and PVC.

These are applied by feeding granules of the material into the nip between moving heated rollers.

This method can apply resin (in the form of films) to fabric at a faster rate than that can be achieved by transfer coating or direct coating.

This process is used to produce light weight coverings or tarpaulins.

CALENDER COATING

Calenders are primarily used to produce unsupported films of PVC and rubbers from compounded polymer ‘dough’.

This process can also be adapted to apply freshly produced film to fabric. Calenders consist of a number of massive rollers. Rollers rotate to crush the ‘dough’ and smooth it into films of uniform

thickness. The thickness of the film is determined by the gap separation of the rollers. The more rollers, film produced is more accurate.

ROTARY SCREEN COATING

The rotary screen technique applies to a fabric by forcing it through a cylindrical screen, it is used mainly for textile printing.

The technique can also be used for coating polymer onto fabric with add-ons in between 5 and 500 g/m2.

The add-on is controlled by : Resin viscosity, Mesh of the cylindrical screen, Speed ,and Pressure of the squeegee bar inside Screen .

SPRAY COATING

A coating material can be sprayed directly onto the substrate surface.

Spray coating methods are: Pressed air vaporization, Airless pressure spray, Hot vapour impelled spray , Electrostatic spray and Dry powder resin spray.

The most common method is compressed air vaporization, where air and coating materials are pressed out through a nozzle.

Limitations Lack of uniformity and precision of application Occasional blocking of spray nozzle

Fig: Spray coating machine

DRY POWDER COATING There are two processes in this category,

1. scatter coating and, 2. dot coating. These processes are used for coating fusible polymer powder i.e , polyethylene,

polyamide, polyester, and Ethylene-vinyl acetate (EVA). The products are used for fusible interlinings, carpet backcoating, especially in

the automotive industry for contoured car carpets, and for lamination. Scatter coating process, polymer powder of 20–200 µm size is spread uniformly

onto a moving textile substrate. The web is then passed through a fusion oven and calendered. The coating weight is dependent on feed rate and web speed.

Powder dot coating process, a heated web having a surface temperature slightly less than the melting point of the polymer is brought in contact with an engraved roller embedded with dry powder. The web is thus coated with a tacky polymer powder in a pattern dependent on the engraving. The engraved roller is kept cool to prevent the polymer from sticking to the roll.

CURTAIN COATING

In curtain coating the coating fluid forms a freely falling liquid sheet and is deposited onto a moving substrate as shown in figure.

No friction is involved so the coating fluid is not forced to penetrate the substrate structure but follows its surface to form a film.

This method is capable of producing a thin film with a range of few microns and the film thickness is not affected by substrate roughness.

Preventing air entrapment and establishing stable fluid curtains are the keys to achieving quality curtain coating.

SLOT DIE OR EXTRUSION COATING

In this method plasticized coating compound is pressed through a sheeting die and transferred directly onto the substrate to be coated.

In the traditional slot die coating system the die lip is in contact with the substrate and backed by the roller which imparts pressure on the substrate.

This is called a closed system, where there is no contact between the coating materials and the air.

MAYER ROD COATING

In this method, compound is applied on the web by a single-roll applicator.

The coating is post-metered by a wire wound rod, known as the Mayer rod that removes excess coating.

An excess of the coating is deposited onto the substrate as it passes over the bath roller.

The wire-wound metering rod, sometimes known as a Meyer Rod, allows the desired quantity of the coating to remain on the substrate.

The quantity is determined by the diameter of the wire used on the rod.

KISS ROLL COATING

The coating is applied on the web as it touches the nip-to-nip of the applicator roll.

The pickup roll may be rubber covered, and the applicator roll made of steel.

The metering is done by nip pressure, and consequently, the amount of material coated on the web is dependent on nip pressure, speed of the operation, roll hardness, and its finish.

GRAVURE ROLL COATING

Engraved dots or lines of the engraved roller fill with the coating material.

The excess coating wiped off by the Doctor Blade.

The coating deposited onto the substrate as it passes between the Engraved roller and a Pressure Roller.

REVERSE ROLL COATERS The coating material is measured onto the applicator

roller by precision setting of the gap between the upper metering roller and the application roller below it.

The coating is 'wiped' off the application roller by the substrate as it passes around the support roller at the bottom.

4-roll versions are more common than 3 roll versions.

REVERSE ROLL COATERS

APPLICATIONS

Agriculture Construction Clothing Geotextiles Home Furnishings Industrial Medical

Transportation Sport/Leisure Packaging Protective

APPLICATIONS FOR COATED FABRICS

Agriculture - Bulk containers, Fencing, Seed/crop covers, Bags, Irrigation systems, Pond liners.

Construction - Safety fencing, wind cover, Safety vests, Hose, Conveyer Belting, Drainage ditches, Architectural Structures.

Clothing - Shoe uppers and linings, Artificial leather, Rainwear ,Garment linings, Water/stain, repellants, Gloves, Hats.

Geotextiles - Settling pond liners, Irrigation liners, Landfill liners & covers, Soil stabilizers, Erosion barriers.

Home Furnishings – Upholstery, Trim, Carpet backing, Drapery backing, Bedding, Artificial leather.

Industrial - Conveyor belts, Filtration, Barrier materials, Field covers.

Medical – Implants, plaster, Gloves, Upholstery.

Transportation - Seating/Trim for, automotive, trucks, aircraft, buses, Belts,Tires, carpet, airbag.

Sport/Leisure - Athletic shoes, Artificial leather/bags/belts, Rainwear, football.

Protective – Gloves, Aprons, Chemical Suits, Footwear Space Suits, Ballistic Protection.

Packaging - Bulk containers,Gas holding, Barrier packaging, Liquid bulk storage/hauling, Waterproof materials

ADVANCED COATING POLYMER

In today’s era the requirements of human beings has been totally changed , so research is going on to achieve human needs .

Some of such achievements are phase change coatings, conductive coating, anti- bacterial coating etc.

After all introduction of nanotechnology has changed the thinking. Some of those are discussed below.

ADVANCED COATING TECHNIQUES

Atmospheric Plasma Coating Phase Change Material Coating

ATMOSPHERIC PRESSURE PLASMA COATING

Water-repellent and self-cleaning coatings can be produced with the aid of atmospheric-pressure plasma processes.

The basis of these coatings is aA microstructured surface which has been provided with a hydrophobic top layer.

PHASE CHANGE MATERIALS Phase change materials (PCM) take advantage of latent heat that can

be stored or released from a material over a narrow temperature range. Working principle of PCM :

Figure . Change in phase change material with the change in temperature.

This interesting property of PCMs would be useful for making protective textiles in all-season. fibre, fabric and foam with PCMs could store the heat body creates then release it back to body, as it needs.

Coating, lamination, finishing, melt spinning, bi-component synthetic fibre extrusion, molding, foam techniques are some of the convenient processes for PCMs’ incorporation into the textile matrix.

Phase change material

SMART TEXTILES

Smart Textiles

PasssiveEx.Conductive fabric

ActiveEx .PCM , SMM

UltraEx.-Musical Jackets

SMART TEXTILES: Conductive Coating

Polypropylene (PP) and viscose (VS) were modified by the insitu synthesis of a conducting Polypyrrole (PPy) overlayer.

To improve adhesion of the conducting layer to the textile surface a Pyrrole-functionalized silane (SP) was synthesized and bonded onto the surface before Polypyrrole formation.

To introduce hydroxyl groups into the surface PP was pretreated by grafting vinyltrimethoxysilane by means of a radiofrequency plasma discharge.

In the case of Polypropylene the effect of pretreatment with SP is much better than for viscose.

Higher concentration of SP leads to improved fastness of the conductive layer which indicates that the coating promoted by means of SP is more favoured than for viscose.

Flame Retardancy

• Two types of Di-ammonium hydrogen phosphate (DAHP) microcapsules based flame retardent with respectively:

1. Polyether- polyurethane shell, and 2. Polyester-polyurethane shell, were evaluated as intumescent flame retardant (FR) in a commercial poly-urea coating for textilesThe advantages of this new concept of encapsulated FR agent are to be compatible with a polymeric matrix in order to give a permanent FR effect and to be itself an efficient FR intumescent formulation for many materials.

Antibacterial Coating

• A novel antibacterial coating for cotton fabrics has been developed using core-shell particles that consist of poly (n-butyl acrylate) (PBA) cores and chitosan shells.

Spherical particles are prepared via a surfactant-free emulsion copolymerization.The PBA-chitosan core-shell particles have a narrow particle size distribution with average particle diameter of approximately 300 nm, and display highly positive surface charges.The cotton fabric is coated with PBA-chitosan particles by using a conventional pad-dry-cure method.PBA-chitosan particles demonstrates an excellent antibacterial activity with bacterial reductions more than 99%.

ULTRA-EVER DRY COATING • Ultra-Ever Dry is a superhydrophobic (water) and

oleophobic (hydrocarbons) coating that will repel most water-based and some oil-based liquids.

• Ultra-Ever Dry uses proprietary omniphobic technology to coat an object and create a surface chemistry and texture with patterns of geometric shapes that have “peaks” or “high points”. These high points repel water, some oils, wet concrete, and other liquids unlike any other coating.

• High adhesion and abrasion resistance.• Translucent White colour coating by xylene(top)and

acetone(bottom) or nano composite polystyrene, Zinc oxide polystyrene (ZnO/PS) nano-composite.

Ultra-Ever Dry Features• Anti-Wetting-

– The superhydrophobic coating keeps objects dry. Water and many other liquids are easily repelled.

• Self-Cleaning - – Repels dirty water and some oils, and remains clean and

virtually bacteria-free. – Dust, dirt or other molecules accumulate on

superhydrophobic coated surface, a light spray of water or a blast of air grabs the dust and removes it.

• Applications:- • Ultra-Ever Dry can be used : Fabric Protect from acids/bases,

Fabrics used in Boats & marinas, Water /oil proofing fabrics etc.

APPLICATIONS OF ADVANCE COATED TEXTILES

Comfort wear Heat protection Medical applications Military applications Computing textiles Fashion Space research

CONCLUSION The coating and lamination gives a powerful tool for the

advancement of textile technology. It provides the opportunities to produce the special fabrics like

water-proof resistant tarpaulins, coverings, large tents and architectural uses, backcoating for upholstery including autoseats, Food packaging, Medical applications, parachutes, Woven curtains for heat- sensitive fabrics, automotive fabrics, disposable hospital apparel etc.

The recent developments also enhanced the lamination and coating technique into state-of-art process of the future in textile field.